1. Field of the Invention
The present invention relates to disc braking systems and more particularly to a distortion reducing technique for affixing a disc brake rotor to a rotatable wheel hub.
2. Description of the Related Art
Many motor vehicles include disc brake systems having a circular metal disc brake rotor with opposed braking surfaces that are clamped by brake pads carried by a brake caliper to exert a braking effect. The wheel hub incorporates an anti-friction wheel bearing assembly in which one race of the bearing is coupled to the vehicle suspension and the other rotationally mounts the brake rotor and wheel. Ordinarily the rotating components of the rotor, wheel and hub assembly are manufactured separately and assembled together by a plurality of bolts and lug nuts which clamp the wheel to the hub flange with a so-called hat or mounting flange portion of the rotor clamped therebetween. In order to enhance performance of the braking system it is desired to carefully and accurately control the dimensional characteristics of the rotor braking surfaces as the rotor rotates. The thickness variation of the disc and the lateral run-out or lateral deflection of the surfaces as they rotate needs to be held to minimum tolerances. The desire to control lateral run-out of braking surfaces of a disc rotor are well known and rotor manufacturing techniques have been improved to reduce such run-out.
For example, U.S. Pat. No. 5,988,761 teaches a wheel end hub assembly for a motor vehicle incorporating mechanical retention features which accurately and positively orient the motor vehicle brake component, such as a disc brake rotor or brake drum with respect to its wheel hub. With this approach, the machining operations for the brake component braking surfaces can be accurately based from a datum surface of the hub. The assembly incorporates a retention nut threaded onto the wheel mounting bolts which exerts a clamping force on the brake component, e.g., a rotor mounting flange, and further establishes the relative positions of the hub and brake component. In this patented arrangement, the wheel is fixed to the hub with lug nuts engaging the mounting bolts and clamping the wheel against the braking component.
U.S. Pat. No. 6,988,598 points out that in conventional disc brake systems, the rotor is generally rigidly attached to the wheel or hub. With this type of attachment method, the rotor run-out must be generally controlled within approximately 0.003 inches to 0.005 inches. Some racing vehicles, such as used in some classes of drag racing, utilize specialized racing aluminum wheels and the rotor must be mounted directly to such wheels. However, these wheels often do not have a mounting surface that runs true enough to mount the rotor within the permissible range of run-out without additional machining. This additional machining requires additional work time and expense and can reduce the strength of the wheel. To solve this problem, the patented device allows the rotor to slide axially during brake application assuming a new axial location not dictated by the wheel face after release of the braking pressure. This patent suggests a disc brake rotor mounting system that enables self-alignment of the rotor without the need for a precision mounting surface on the wheel. In a preferred embodiment, a generally circular wheel adapter is adapted for mounting to a surface of a hub or wheel with fasteners engaging the hub or wheel through a plurality of wheel attachment bores spaced around a circumference of the wheel adapter. The wheel adapter includes a plurality of drive pin bores spaced around its circumference through which drive pin attachment bolts can be inserted to threadingly engage a like plurality of drive pins. The drive pin attachment bolts securely fasten the drive pins to the wheel adapter. The brake rotor includes a plurality of radially aligned drive slots positioned to align with the plurality of drive pins. Alignment bushings mount between each of the rotor drive slots and a corresponding drive pin. The alignment bushings include a central channel and a pair of flanges. The raised flanges slidingly engage opposing sides of the brake rotor and axially retain each alignment bushing with respect to its corresponding drive slot.
In operation during braking, calipers press on the brake rotor causing torque on the brake rotor resistant to the rotation of the wheel to which the brake rotor is attached. This torque is transmitted as force through the alignment bushings to the drive pins and so on to the wheel itself. As the calipers grip on the brake rotor, any misalignment of the brake rotor will result in the calipers exerting greater force on one or the other side of the brake rotor. In such a case, once the net force on the brake rotor overcomes the resistance of the drag rings, the brake rotor will slide in or out on the drive pins until located such that the calipers exert the same force on both sides of the brake rotor. Once the braking operation subsides and the calipers no longer exert any force on the brake rotor, the brake rotor stays fixed in its new location and orientation due to the drag rings. Neither of these patented arrangements recognizes that rotor brake plate run-out can increase on the vehicle due to mounting flange distortions that occur when the wheel contacts the rotor flange as it attaches to the hub, let alone suggesting any solution to such a problem.
It is desirable to minimize mounting induced rotor lateral run-out along with other sources of lateral run-out.